Degradation of pectin by γ‐radiation under various moisture conditions

By using D50 and D37 doses for 50 and 63% decreases in the solution viscosity of pectin, an evaluation was made of the effectiveness of radiation at different moisture levels. The relation between radiation effectiveness, as measured by the D50 value, and the pectin: water ratio was expressed in a simplified empirical equation. The indirect effect of radiation in dilute aqueous solutions decreased progressively with increasing pectin concentration. On the other hand, a protective effect was produced by small additions of water to dry pectin and a minimum in degradation (i.e., maximum D50 and D37 values) was attained at about the 20% moisture level. The relation between the intrinsic viscosity of dilute aqueous solutions of pectin irradiated air‐dry and the number‐average molecular weight and D37 values was determined. By using the former relation, the number of chain scissions per unit of absorbed energy was measured at different moisture levels. The importance of moisture control in comparative radiation studies was emphasized. An approximately 26‐fold increase in the radiation sensitivity of pectin was produced by an increase in the moisture content from the 20 to the 99% level. Varying the moisture content therefore provides a good means of altering the sensitivity of pectin and similar materials to radiation damage.